A complete monkey brain atlas of the localization of catecholaminergic neurons (cell bodies and nerve terminals) and serotonin-containing cell bodies has been prepared. From a comparative standpoint it is clear that a striking similarity exists in the localization of catecholamine- and serotonin-containing cell bodies between the monkey and the rat. These and other comparative data indicate that a prototypical pattern of organization of aminergic systems has been retained in the evolution of primates. Stereotaxic maps of noradrenergic pathways (dorsal and ventral bundles) in the rat brain have also been prepared. BIBLIOGRAPHIC REFERENCES: Jacobowitz, D.M., and MacLean, P.D.: A brainstem atlas of catecholaminergic neurons and serotonergic perikarya in a pygmy primate (Cebuella Pygmaea). J. Comp. Neurol. (In Press) 1977. Jacobowitz, D.M.: Monoaminergic pathways in the central nervous system. Psychopharmacology: A Generation of Progress, 1977 (In Press).